The present invention relates to electronic processing of exposed photographic material. In particular, this invention relates to the use of a radio frequency photoconductivity measurement to scan a photographic element to detect a latent image in the exposed photographic material.
The latent image in silver halide crystals is formed through the excitation of free charge carriers by absorbed photons and their subsequent trapping and reaction with interstitial silver ions within the silver halide grain structure to form latent image centers (i.e. electron trapping centers). The use of electromagnetic radiation to detect latent image formation in exposed silver halide grains has been recognized in the photographic art. For example, the January/February 1986 issue of Journal of Imaging Science, Vol. 30, No. 1, pp. 13-15, in an article entitled xe2x80x9cDetection of Latent Image by Microwave Photoconductivityxe2x80x9d, describes experiments designed to detect latent image formation in silver halide using microwave photoconductivity. The technique, which is operated at room temperature, is recognized as potentially useful in detection of latent images without the need for conventional chemical development solution processing.
Carriers which are thought to play an important role in the formation of latent image centers in silver halide grains are believed to be electrons, holes, and interstitial silver ions. The mobility of electrons is far greater than that of holes or interstitial silver ions so that conductivity attributed to photoelectrons is expected to be detectable by measurement of photoconductivity of silver halide grains through use of microwave radiation. Such a measurement has been reported using low temperatures, L. M. Kellogg et al., Photogr. Sci. Eng. 16, 115 (1972).
U.S. Pat. No. 4,788,131, issued Nov. 29, 1988 to Kellogg et al., entitled xe2x80x9cMethod of Electronic Processing of Exposed Photographic Materialxe2x80x9d discloses a method for electronically processing exposed photographic materials for detection and measurement of latent images contained therein. The method includes the steps of placing the element in an electromagnetic field and cooling the element to a temperature between about 4 to about 270K to prevent further image formation; subjecting the element to a uniform exposure of relatively short wavelength radiation; exposing the element to pulsed, high intensity, relatively longer wavelength radiation to excite electrons out of image centers; and measuring any resulting signal with radio frequency photoconductivity apparatus.
The shortcomings of this approach are that it needs to be performed at low temperatures, and there is no easy technique disclosed for making a two dimensional scan of the element.
Accordingly, there is a need for an improved technique for detection and measurement of latent images in silver halide photographic materials.
The need is met according to the present invention by providing a method of electronic processing of a latent image from a photographic element, the method employing pulsed radiation and radio frequency photoconductivity apparatus having a sample capacitor with a gap, that includes the steps of: placing the element in an electromagnetic field adjacent the sample capacitor; providing an advance mechanism for advancing the photographic element past the capacitor; scanning the element through the gap in the sample capacitor with a pulsed, focused beam of radiation; directly measuring the photoelectron response of the element and recording the resulting signals from the radio frequency photoconductivity apparatus; and advancing the element and repeating the exposing and measuring steps to provide a two dimensional readout of the latent image on the photographic element at ambient temperature or below.
In a preferred embodiment, the photographic element has a Ruthenium hexacyano doped tabular grain emulsion with a grain size greater than 2 xcexcm, and the measurement of the photoelectron response is conducted at ambient temperature.
The present invention has the advantage of eliminating the need for chemical processing of photographic film for development. A simpler film format can be employed with the present invention that does away with the need for dispersions or interlayers, thereby simplifying and reducing the cost of the film manufacturing process. Only one emulsion per color is required since the resulting signal from individual silver halide grains is proportional to the exposure level of the grain.